Silicon single crystals are formed into silicon wafers by mechanical processes such as grinding and cutting. For example, in the case of a grown rod of the silicon single crystals, the outer surface of the rod is first ground, and cut into cut rods each having such a predetermined length as to be easily handled. Then, the cut rods are subjected to a slice process to obtain the wafers.
During the grinding or cutting (silicon processing) of the grown rod of the silicon single crystals, grinding water such as industrial water, well water, city water or pure water is used. Therefore, silicon processing wastewater which takes place during the silicon processing contains a large amount of silicon processing waste constituted of fine powder of silicon. When this silicon processing wastewater is discarded or reused, the contained silicon processing waste needs to be separated, and hence it is general to perform a filter treatment by use of a wastewater treatment system including various filters.
As related conventional technologies, there are disclosed a wastewater treatment method of injecting a specific acid component into the silicon processing wastewater as a treatment target to acidify the wastewater and then filtering the wastewater through a filter membrane to suppress the formation of components which clog the filter membrane, and a treatment system (e.g., see Patent Documents 1 to 3).
Patent Document 1: JP-B-6-69551
Patent Document 2: JP-A-2002-50596
Patent Document 3: JP-A-2005-21805